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 Post subject: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 5:34 am 
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Location: Oberhausen, Germany
Hi everybody!

After years of silently stalking this forum I finally decided to sign up and start building my own puzzles.
As I started reading years back I'm asking myself why most of the "old" methods seem to be abandoned. Nowadays most puzzles are completely 3D-printed and I haven't seen many people posting about cast puzzles.

Therefore, I wanted to see if just printing masters and casting them was still a viable option.
As such I have a few questions about tolerances and minimal sizes for parts.

I read somewhere that 2mm fillets where a good idea and that parts printed using FDM shouldn't be shelled less than 2mm thick. I concluded that 4mm per "layer" would be a good starting point.
After discarding FreeCAD for its inability to correctly fillet complex parts, I opted for AutoCAD as I'm a student. After a slight learning curve designing became quite easy :).

Here is a picture of a triangular piece with 3 "layers" with the middle one slightly shifted, which is the flimsiest part of my current design:
Attachment:
File comment: Triangle piece
triangle2.png
triangle2.png [ 38.35 KiB | Viewed 1945 times ]

I'm planning on printing the masters through shapeways with SLS in WSF polished and then casting them with polyurethane resin.
I'm pretty sure the parts are sturdy enough as it is, but can I reduce the "layer" thickness without running into problems while casting?
What should the maximum height of the puzzle be?
Do I even need to add tolerances to the parts, if I order them in polished?
If not, how much tolerances should I add and should I add them to all interacting surfaces or just the one's that are not gliding on one another?
Some parts have symmetry and can thus be split into equal parts to reduce printing cost. As hollow pieces are difficult to cast otherwise, this would also reduce the total weight and material used. Are the typical tolerances on cast pieces to big for assembling—say—a three-part corner?
As seen above I have tried to make a compromise on the shifted layers, so that the "lip" (protruding edge of the middle layer) and the "stem" (section of the three layers, when projected on a sphere) are about equal (which is 6 degrees in the cut line). Is this a good compromise or should I focus more on the lip or stem?

Also, I plan on printing some masters using a home FDM printer in the future. Any thoughts on the work needed to make these masters usable? I'd sand them down, polish them and smooth them with solvent, naturally.

The part is not filleted for now as I'm still experimenting with layer thickness and cut appearance on the outside.
If any of these questions have already been answered, I'm sorry. I searched all over the forum but couldn't find any specific answers.

Thanks in advance for any answers!

Briac


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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 7:18 am 
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I can't answer most of your questions as I have no experience with casting puzzle parts. But, I would say that Tony Fisher is the go to person for casting questions, as he has been doing it since Noah was a lad.

As to using WSF as a mould master: WSF (nylon) has, in its natural state, a very rough and porous surface, which will make the mould material stick to it. Also, depending on what temperature the material cures at, you would have to be careful not to get the WSF too hot so that it deforms and ruins the mould. You could try WSF polished, but you will have to take into account that the polishing process removes some material. You may be able to prepare (sand? coat?) the WSF yourself as well.

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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 9:01 am 
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I was planning on the polishing process removing material to implement the "tolerances" ie some space between the pieces, which I would otherwise have done directly by having a slightly offset cut-curve surface shaving of some more of the pieces (tenths or less of a millimeter).

Yeah, I kinda figured there wouldn't be many people jumping to answer this questions, but maybe some of the "old masters" might come by ^^.


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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 10:01 am 
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The polishing alone will not create enough tolerance. I typically create a .3mm gap between two layers of the shell. I imagine (from my limited experience) that with casting you will need more.

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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 2:25 pm 
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This may be a little off topic for your question, but what was your problem with the filleting on FreeCAD? I'm guessing it was these points?

Those points are just plain trouble. However, if you add tolerances into your design (rather than relying on polishing), that problem should go away.
When you add tolerance, those shells no longer touch, so you have to build a spacer in between them. That gives the program an actual edge to fillet instead of a zero-length point.

Also, Drewseph posted this back in '09 showing where tolerances should lie. You've gotta click on the image in his post to see the correct tolerances.
viewtopic.php?p=193097#p193097


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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 5:17 pm 
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I did not model this particular design in FreeCAD, as I ran some test on simpler models. E.g. I modeled a core-less 3x3 (like a void cube without windows looking in). Filleting problems appeared everywhere a "radial" edge met perpendicularly with a sphere section (i.e. a stem and to layers). Using very small fillets (<1 mm) I could fillet most edges, but going higher I had problems with dissappearing layers of the solid, which made it into a shell I could not fix. I gave up after trying to find a workaround. Also, FreeCAD's boolean operations aren't great. Out of 5 methods for making a part only one seemed to work, the others throwing errors.

Thanks for the input!
I'm not quite sure what to think here. TomZ says he adds an 0.3mm tolerance between his shells (of which by my definitions my design has either just one or three), but Drewseph and Oskar (in his article on designing twisty puzzles) say you need 0.2mm on "jamming" faces and 0.4mm where pieces hang, but none where pieces slide on one another and at the outside "extensions" of the puzzle (where the sphere becomes the solid). It's difficult to decide what applies for my design or which "school" of design I should follow ;). ... I'd guess I should shave down between the middle layer and the bottom layer (or the top layer?) as well as on the "jamming" faces of the middle layer. I'll go with 0.4mm for now unless I get a definite answer.

I'm toying with reducing the layer thickness to 3mm. Would any obvious reasons stand in my way on that? As of now the height is about 80mm making it about as tall as a skewb kite, which shouldn't be to much, I think.
Currently trying to find a nice cut-curve for a curvy cut, as radial cuts don't do much on the solid. Any pointers on avoiding overhang bandaging with to extravagant "external" cut-curves?

I have not yet thought about the curing temperature of the mold. The shapeways materials page says WSF should be safe up to 80°C and I found some silicone-based molding solutions that claim to vulcanize at room temperature without much heat production, which should work for my purpose. As a byproduct of the mold curing, the silicone gases out ethanol. I do not think that would be a problem as nylon is (as far as I know) insoluble in (and does not react with) ethanol. I'm also quite sure people have already cast puzzles from SLS WSF printed puzzles, though I don't have a link.

Briac

PS: Yeah, those points are quite some trouble with AutoCAD, too. But I found I could just ignore that the two "adjacent fillets wouldn't meet exactly at the points. I don't see any parts jamming on the little resulting edges.


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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 8:28 pm 
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Buriaku wrote:
I have not yet thought about the curing temperature of the mold. The shapeways materials page says WSF should be safe up to 80°C and I found some silicone-based molding solutions that claim to vulcanize at room temperature without much heat production, which should work for my purpose. As a byproduct of the mold curing, the silicone gases out ethanol. I do not think that would be a problem as nylon is (as far as I know) insoluble in (and does not react with) ethanol. I'm also quite sure people have already cast puzzles from SLS WSF printed puzzles, though I don't have a link.

You will be fine with silicone rubber. I am not aware of any getting hot.

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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 10:01 pm 
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If you plan on post-processing the SLS (polishing) then it should be relatively easy to just manually fillet the master piece with sandpaper or a file. So if your CAD isn't cooperative, ignore it!

I don't have any experience casting from SLS masters, and don't recall reading much about it. I would encourage you to take your time and make the masters as perfect as you can, however.

Silicone rubber molds break down over time and any roughness in the mold will accelerate this. So if you start from a porous and slightly rough surface you want to get it as smooth and shiny as you can before you make your molds to aid repeated removals.

I document doing this for FDM parts (much rougher) here.

Good luck, and post with your progress!

Dave

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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 20, 2013 11:38 pm 
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It's great to see someone getting into casting. It was really an enjoyable facet of this hobby for me, and I haven't given up on using it again.

Having cast a lot of puzzles, I would really recommend using shapeways detail (obJet) for masters. The roughness of SLS will be magnified in the more rigid urethane cast, and Nylon doesn't sand well in my experience.

As others have said, polishing won't give you the tolerances you need.

Your 4mm layer thickness is great but not necessary.
2mm is fine for shell thickness.
A "neck" or connection between shells should have a line you can draw in the cross section that's 4mm across somewhere even if it's not round. Short necks can be 2mm in Nylon, but I wouldn't try that in urethane.
2mm radius where shells interact. Real life prevents 2mm sometimes.
0.7-0.8mm radius on the top and bottom of shells.


It's impossible to state a fraction of the molding gotchas in this thread, but the puzzle building forums in 2008, 2009 should be a goldmine.

Oh... Don't improvise on silicone mold release.

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 Post subject: Re: Questions about masters for casting
PostPosted: Wed Aug 21, 2013 6:30 am 
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Thanks again for the great answers.

JasonSmith wrote:
Having cast a lot of puzzles, I would really recommend using shapeways detail (obJet) for masters. The roughness of SLS will be magnified in the more rigid urethane cast, and Nylon doesn't sand well in my experience.

Does the remaining roughness of polished Nylon really reflect that much in the mold? What kind of "detail" material do you mean? There's "Detail Plastic" and "Frosted Detail Plastic" on their materials page. Both seem not to be printed using SLS but some nozzle type printing. They state that Frosted Detail has more smoothness, while Detail has more strength. I don't think the strength will be a problem at my wall strengths, but they want parts to be sprewed for Detail Plastic if I have more than five parts (which astonishingly I have!). Do they insist on this? Also these Materials don't profit from tightly packing the STL file, if I understand their pricing model right. How should I orient my pieces for optimal printing in either of these materials?

JasonSmith wrote:
2mm radius where shells interact. Real life prevents 2mm sometimes.
0.7-0.8mm radius on the top and bottom of shells.

I can't follow you here. Do you mean fillets in both these statements? Is the second one tolerances? Or both?

JasonSmith wrote:
Oh... Don't improvise on silicone mold release.

I don't know what you're insinuating. ... I was planning on thinly coating the molds with vaseline before casting. ... Is this not a good idea? Or could i use the silicone spray I use for lubing my cubes ^^?

Briac


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 Post subject: Re: Questions about masters for casting
PostPosted: Wed Aug 21, 2013 4:45 pm 
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Buriaku wrote:
I was planning on thinly coating the molds with vaseline before casting. ... Is this not a good idea? Or could i use the silicone spray I use for lubing my cubes ^^?

Briac

A release agent should be used when making the actual moulds, not when casting. Silicone rubber has a "built in" mould release. If you do decide to use one though make sure it's something recommended. Other wise there's a very good chance you will end up trying to wash a sticky gooey mess out of your moulds.

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 Post subject: Re: Questions about masters for casting
PostPosted: Thu Aug 22, 2013 1:56 am 
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I think the rough nylon will really show up. You'd have to do a ton of prep on every part you cast to get a nice puzzle, if you ever can. I can't advocate enough using great masters for casting. It's a lot of work, and the effort is about the same for a great puzzle or a bad puzzle, depending on the masters.

The original Petaminx required sanding of every cast part to make it work, which was horrible. I hadn't prepared the parts carefully enough for casting. They seemed somewhat smooth, but weren't really. And they were obJet (detail material).

I haven't used the detail materials recently, except for my Silver orb beads, which didn't seem to require sprues. But maybe I slipped through the cracks!

The quantity discounts are great, but are less important in masters than they are in trying to print a full puzzle.

And yeah, vaseline as a release when pouring the silicone molds is great. (I've sealed molds shut making them with the wrong release before.)

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 Post subject: Re: Questions about masters for casting
PostPosted: Thu Aug 22, 2013 2:39 am 
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JasonSmith wrote:
And yeah, vaseline as a release when pouring the silicone molds is great. (I've sealed molds shut making them with the wrong release before.)
Mann Easy Release 200 has not failed me with OOMOO 30.

Dave

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 Post subject: Re: Questions about masters for casting
PostPosted: Tue Aug 27, 2013 7:34 am 
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Tony Fisher wrote:
A release agent should be used when making the actual moulds, not when casting. Silicone rubber has a "built in" mould release. If you do decide to use one though make sure it's something recommended. Other wise there's a very good chance you will end up trying to wash a sticky gooey mess out of your moulds.
Oops, I remember making the same error, when reading the forums years ago—not thinking about a release between two mold halves, that is. Thanks for reminding me. I will opt for a "silicone-free release agent" in a spray can, I think.

JasonSmith wrote:
I think the rough nylon will really show up. You'd have to do a ton of prep on every part you cast to get a nice puzzle, if you ever can. I can't advocate enough using great masters for casting. It's a lot of work, and the effort is about the same for a great puzzle or a bad puzzle, depending on the masters.

The original Petaminx required sanding of every cast part to make it work, which was horrible. I hadn't prepared the parts carefully enough for casting. They seemed somewhat smooth, but weren't really. And they were obJet (detail material).

I haven't used the detail materials recently, except for my Silver orb beads, which didn't seem to require sprues. But maybe I slipped through the cracks!
At first I was dead set on using WSF for my masters even if I had to fill the roughness with milliput and spend ages sanding, but you convinced me not to. As such I chose the "Frosted Ultra Detail" option as it was just a few dollars more than "Detail" or normal "Frosted Detail" (and the shipping costs makes the cost differences quite negligible for just my small set of masters). The extra detail might make sanding easier, who knows? I thought I shouldn't hold back my money on my first casting try and start from the best material available (at a sensible price).
I might try with WSF in the future, though.

DLitwin wrote:
Mann Easy Release 200 has not failed me with OOMOO 30.
Dave
Living in Germany I unfortunately do not have convenient access to Smooth-On or Alumilite products. I think I have found suitable replacements though.

I'll report back, if I ever get any positive results ^^.

Cheers,
Briac

Edit:
For posterity, I switched from AutoCAD to Inventor, as AutoCAD couldn't cope with more complex fillets than the ones that failed in FreeCAD. Also AutoCAD doesn't do parametric cut curves well. Inventor is far from perfect, though. You can't cut a solid by more than one surface at a time and some splits just won't work. ... All in all it's very useable though and I hear Solidworks has its flaws, too.


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 Post subject: Re: Questions about masters for casting
PostPosted: Sat Aug 31, 2013 12:19 am 
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Buriaku wrote:
Living in Germany I unfortunately do not have convenient access to Smooth-On or Alumilite products.

What about this?
http://www.kaupo.de

Produktkatalog -> Silikonkautschuk
Produktkatalog -> Polyurethangießharz


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 Post subject: Re: Questions about masters for casting
PostPosted: Sat Aug 31, 2013 4:58 am 
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Andreas Nortmann wrote:
Buriaku wrote:
Living in Germany I unfortunately do not have convenient access to Smooth-On or Alumilite products.

What about this?
http://www.kaupo.de

Produktkatalog -> Silikonkautschuk
Produktkatalog -> Polyurethangießharz

Or http://www.gestaltungsmaterialien.de/pr ... /index.php

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Buy my mass produced puzzles at Mefferts:
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 Post subject: Re: Questions about masters for casting
PostPosted: Sun Sep 01, 2013 3:46 pm 
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Danke, Andreas! Dank je wel, Tom!

I knew about KauPo, but I'm suspicious about their business. I've looked at their site some (3? 4?) years ago ... and they still haven't updated to include an online shop. ... That's just weird.

I hadn't found gestaltungsmaterialien.de yet, though I can't say I like their prices. ... Also, I have seen several people complaining that Smooth-On products were overpriced and didn't work as well as other products *shrug*.

I will try with products from bacuplast-shop.de at first. If those shouldn't fit my purpose, I'll still be able to switch to another brand.

My project is all about making a puzzle for the least price using "cheapest" material, needing the least amount of plastic and using the most efficient mechanism (smallest amount of non-visible parts). Also I'm aiming for designs that might be suitable for mass production, as I've seen many awesome puzzles that may never be widely available due to complexity of the mechanism. We'll see if I'm going the right way. (Using FUD instead of DP or WSF was a decision to prolong mold life and getting better detail ;).)

Briac


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 Post subject: Re: Questions about masters for casting
PostPosted: Wed Sep 18, 2013 7:27 pm 
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Well, I said I'd report back, if I had any positive results :).

Freshly hatched:
Attachment:
File comment: Freshly hatched clickless V-Cube 6 hidden edge center piece with mold and original
freshly_hatched.jpg
freshly_hatched.jpg [ 40.19 KiB | Viewed 1323 times ]


I lost a hidden edge center piece of my modded V-Cube 6 some years ago and just had not gotten a replacement for it, so I thought it would be the perfect piece to start experimenting. I think I can pour parts with a thickness of way under 2mm!

I promptly inserted the piece and it works perfectly ... with the exception that the puzzle is stiff as hell ^^. Ever tried wrestling a non-broken-in, clickless-modded (corner and adjacent hidden edges bandaged to the core), freshly lubed V-Cube 6 with your bare hands? It's hard ^^.

I used Drewseph's method with the lip for my mold. The only things that went wrong was me not using enough mold release on one mold and forgetting to shake one of the resins parts before using ^^', which led to a have shut mold and a weird alien piece consisting of a skin with liquid inside, which was still flexible *shudder*.

The molds are very promising with very few air bubbles and the resin flows nicely into every crevace.

As my stickers have already arrived courtesy of Olivér Nagy, I may be able to present the puzzle in 1-2 weeks, if no further difficulties arrise (which is uncertain) ;). So stay tuned.

Briac


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 Post subject: Re: Questions about masters for casting
PostPosted: Wed Sep 18, 2013 9:23 pm 
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Buriaku wrote:
My project is all about making a puzzle for the least price using "cheapest" material, needing the least amount of plastic and using the most efficient mechanism

I know your 6x6x6 part was an experiment but you used at least 5 times more silicone rubber than necessary for the mould.

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 Post subject: Re: Questions about masters for casting
PostPosted: Thu Sep 19, 2013 3:44 am 
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It really was too much for that little piece and I used less (per part) for the following moulds. I just mixed to much silikon that first time ^^'.

I'm still experimenting with base thickness and space between puzzle parts. I currently use about 1.5 Legos in height in both directions from the parting line. Thus I have 3 Legos in height for the mould. I'll see if it's "safe" to reduce it even more.

Do you think these base thicknesses are exaggerated? My parts are at most about 1 Lego in height with most of them not thicker than say half a Lego. 1 Lego is 9.6 mm in height, when stacking though that grows to about 1cm.


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 Post subject: Re: Questions about masters for casting
PostPosted: Thu Sep 19, 2013 12:14 pm 
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It depends on a few things. The softness of the silicone rubber you are using, the shape of the part, how many times you will use the mould etc. If the part has a large flat side then I would increase thickness. If however it's a pointy corner you can get away with 1cm or less. If you are using the mould over and over again thin walls will more likely split but that depends on whether that area has to withstand a lot of force when you are removing a part. If you are going for ultra efficiency there are a lot of factors to consider.
Drewseph is the master of this moulding technique but I found the trough unnecessary. I just use keys in the rubber to ensure alignment.

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